Quick Answer
The answer is to use IPsec VPN between the instances. This is correct because IPsec operates at Layer 3, encrypting the entire IP payload of traffic flowing between EC2 instances, regardless of subnet placement within the same VPC. Security groups and network ACLs are stateful and stateless firewalls, respectively, but neither provides encryption; they only filter traffic based on rules. VPC Peering connects VPCs but does not encrypt traffic between instances by default. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of where encryption is applied in the AWS network stack versus simple access control. A common trap is confusing security group rules or VPC Peering with encryption capabilities. Remember the memory tip: “Firewalls filter, IPsec encrypts” — if the question asks for confidentiality between instances, think IPsec, not security groups.
This ANS-C01 practice question tests your understanding of network design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company wants to ensure that traffic between EC2 instances in the same VPC but different subnets is encrypted. Which solution should be used?
Use security groups to allow traffic.
Why wrong: Security groups are firewalls, not encryption.
Use VPC Peering.
Why wrong: VPC Peering does not encrypt traffic.
Use network ACLs to allow traffic.
Why wrong: NACLs are stateless firewalls, not encryption.
Use IPsec VPN between the instances.
IPsec provides encryption for traffic between instances.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use IPsec VPN between the instances.
Option C is correct because IPsec VPN between instances provides encryption. Option A is wrong because security groups do not encrypt traffic. Option B is wrong because NACLs do not encrypt. Option D is wrong because VPC Peering does not encrypt traffic.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use security groups to allow traffic.
Why it's wrong here
Security groups are firewalls, not encryption.
Use VPC Peering.
Why it's wrong here
VPC Peering does not encrypt traffic.
Use network ACLs to allow traffic.
Why it's wrong here
NACLs are stateless firewalls, not encryption.
Use IPsec VPN between the instances.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
The correct answer is: Use IPsec VPN between the instances. — Option C is correct because IPsec VPN between instances provides encryption. Option A is wrong because security groups do not encrypt traffic. Option B is wrong because NACLs do not encrypt. Option D is wrong because VPC Peering does not encrypt traffic.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
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